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This just seems to illustrate the complexity of compiler authorship. I am very sure c compilers are wble to address this issue any better in the general case.
by rhdjsjebshjffn 1y ago
This just seems to illustrate the complexity of compiler authorship. I am very sure c compilers are wble to address this issue any better in the general case.
- runevault 1y agoKeep in mind Rust is using the same backend as one of the main C compilers, LLVM. So if it is handling it any better that means the Clang developers handle it before it even reaches the shared LLVM backend. Well, or there is something about the way Clang structures the code that catches a pattern in the backend the Rust developers do not know about.
- rhdjsjebshjffn 1y agoI mean yea, i just view rust as the quality-oriented spear of western development. Rust is absolutely an improvement over C in every way.
- vlovich123 1y agoThe rust issue has people trying this with c code and the compiler generates the same issue. This will get fixed and it’ll help c and Rust code
- runevault 1y agoOut of curiosity just clang or gcc as well?
- josephg 1y agoI just tried it, and the problem is even worse in gcc. Given this C code: typedef struct { uint16_t a, b; } pair; int eq_copy(pair a, pair b) { return a.a == b.a && a.b == b.b; } int eq_ref(pair *a, pair *b) { return a->a == b->a && a->b == b->b; } Clang generates clean code for the eq_copy variant, but complex code for the eq_ref variant. Gcc emits pretty complex code in both variants. For example, here's eq_ref from gcc -O2: eq_ref: movzx edx, WORD PTR [rsi] xor eax, eax cmp WORD PTR [rdi], dx je .L9 ret .L9: movzx eax, WORD PTR [rsi+2] cmp WORD PTR [rdi+2], ax sete al movzx eax, al ret Have a play around: https://c.godbolt.org/z/79Eaa3jYf https://c.godbolt.org/z/79Eaa3jYf